1. Field of the Invention
The present invention relates to a technique of cutting a substrate into multiple pieces using a heat stress, and more particularly, to method and apparatus for cutting a substrate into multiple pieces with irradiation of a laser beam in which a light beam, generated from a single light generating unit with a specific wavelength and power, is divided into multiple light beams having uniform power, the substrate is locally and rapidly heated by the respective divided beams and then rapidly cooled by a coolant, and thereby the substrate is concurrently cut along plural cutting lines to give multiple pieces.
2. Description of the Related Art
Generally, glass substrate has been widely used for industrial, commercial, and residence applications, to name a few. These glass substrates are made from silicon that is a main component. Also, these glass substrates have a non-crystalline structure that is an inherent characteristic of glass. When a minute groove is formed at an edge of the glass substrate, the non-crystalline structure acts to trigger an occurrence of minute cracks by a small impact or a small external force.
When an external impact or force is applied to the minute cracks, the cracks are propagated along unpredictable directions and therefore an undesired separation occurs in the glass substrate. Thus, there is a problem in that it is nearly impossible to forecast the direction of the generated crack and a portion of the substrate is cut that needs not be cut.
This problem frequently occurs when a diamond cutter is used for the cutting of a workpiece glass substrate in which a fine groove is formed at the surface of the workpiece glass substrate and then some external force is applied. This is because the fine groove formed by the diamond cutter is very rough.
Thus, in the case that the cut groove of the workpiece glass substrate is not smooth, undesired cracks occur additively and the crack propagates along an undesired direction, which causes a fatal failure.
Because of these problems, a diamond cutter is mainly used only as a cutting tool for cutting a commercial glass substrate, a household glass substrate, etc., but is subject to many limitations in a technical field such as a liquid crystal display (LCD) requiring precise cutting.
In spite of these limitations, and since methods and apparatuses for use in the LCD technical field requiring a precise cutting of glass substrates are not yet developed, the use of the diamond cutter is inevitable.
Due to the use of the diamond cutter, there is a problem of unpredictable cracks and the cracks progating when separating a completed LCD mother panel into unit panels.
Accordingly, it is an object of the present invention to provide a method for multiple-cutting a substrate in which a substrate is cut by a heat stress such that an occurrence of cracks is restrained at an edge of the substrate and therefore crack propagation along an undesired direction does not occur.
It is another object of this invention to provide a method for multiple-cutting a substrate in which plural places of the substrate are concurrently and rapidly heated and then rapidly cooled using a single laser beam for heating the substrate, so that the plural places of the substrate are concurrently separated.
It is still another object to provide an apparatus for multiple-cutting a substrate in which a single laser beam for heating the substrate is uniformly divided into at least two beams, the divided beams concurrently heat at least one prescribed cutting line, the heated prescribed cutting line is concurrently cooled, so that plural places of the substrate are concurrently cut.
To achieve the aforementioned objects, there is provided a method of multiple-cutting a substrate. In the above method, a part of an incident light in a first advancing direction is reflected into a second advancing direction and the remaining part of the incident light advances along the first advancing direction to split the incident light into two light beams. The split lights are scanned onto plural selected paths of the substrate to locally heat the selected paths of the substrate. Thereby, cracks are generated at the heated paths.
According to another aspect of this invention, there is provided an apparatus for multiple-cutting a substrate into multiple pieces using a single scanning of a light. The apparatus comprises: a light splitting unit for splitting a light generated from a light generating unit using at least two light reflectivity/transmittance control plates of which light reflectivity/transmittance varies depending on an angle between the generated light and the plates, and for scanning the split lights onto at least two scanning surface portions to locally heat the scanning surface portions; and a crack generating unit for generating a crack at the locally heated scanning surface portions.